RPS, the FTSE 250 consultancy group that is developing its energy services team through acquisitions, reached a deal with Simkins, who founded Oceanfix International in 1981.
Oceanfix provides services for ground surveys mainly in searching for hydrocarbons around the world, both on land and offshore, but the company's expertise is also used in construction.
It has, for example, provided ground surveys for the National Trust for Scotland on Craigievar Castle in Aberdeenshire.
Simkins, whose family owns the company outright, has received an initial payment of 3.9m.
Subject to operations conditions, Simkins will receive payments of 1.3m in 2009 and 2010. He declined to comment on the sale yesterday.
Oceanfix made a pre-tax profit of 1.25m in the year to 31 January, on revenue of 10.6m, with net assets of 1.96m.
According to RPS, Oceanfix will remain based in Aberdeen, with all of its staff, including 58-year-old Simkins, transferring to the employment of its new owner.
The deal is the latest in a string of acquisitions for RPS, which is headquartered in Abingdon, Oxfordshire.
In the past fortnight the company has announced two more deals – to buy engineering consultancy company RW Gregory for 12.1m in cash and shares, and WTW and Associates, a Hampshire- based oil and gas exploration consultancy, for up to 1.85m in cash.
RPS chairman Brook Land yesterday signalled that the spending spree could continue, saying the acquisition pipeline "remains encouraging".